The present invention relates to a shade or color determination apparatus for teeth and dental restorations, and also relates to a method for specifying and determining shades for teeth and dental restorations.
Such a shade determination apparatus and such a method are known from U.S. Pat. No. 5,766,006. This solution represents an advance relative to the use of a conventional shade guide. A commercial shade guide has a plurality of color groups, whereby in each group are located teeth with different color saturation and brightness and each group is assigned to a certain shade. The tooth in a shade guide can have a structure of one to five layers.
Such a shade guide has limited selection options. This limitation is not due to a lack of options for producing different color mixtures, but rather to the fact that even experienced dentists are limited in their ability to determine a shade correctly. One reason for this is that the eye becomes fatigued after long periods of comparison. But it is also due to the fact that the eye must observe the natural tooth and the prosthetic tooth held next to it in the shade guide in an xe2x80x9cintegratedxe2x80x9d manner in order to obtain the results of the comparison. As a rule, the tooth in the shade guide has a two-layer structure and an overall thickness of 5 mm, whereby in the incisal region enamel material is applied thicker and in the cervical region dentine material is applied thicker.
An additional problem in the assessability of the reference teeth in the shade guide is that the teeth in the shade guide regularly comprise ceramics fired at high temperatures. Although such ceramics are more cost effective in terms of manufacture, manufacturing costs are substantial since they have to be distributed to all of the dentists. However, today it is not unusual for other ceramics to be used that are fired at temperatures lower than, e.g., 1300xc2x0. The newest materials for dental restorations always have optical properties that are similar to teeth, e.g. opal effects or brightness values determined by precisely-defined crystal sizes, whereby the optical refraction index is adjusted. Shade guides used in the past are generally not well suited for comparing shades with these new materials. The materials d.SIGN and Empress 2 are also among the new materials that have enhanced brightness even with better translucence. The shade guides that were used in the past are generally not well suited for comparing shades with these new materials.
In this regard, systems like that of the aforesaid US patent are not helpful because they use the known shade guides as the reference. However, since these are not accurate despite the tooth-like structure of their coloration, especially for particularly translucent teeth, such computer-supported systems only result in minor improvements despite the expense they involve.
Another problem that in the past could only be addressed unsatisfactorily, if at all, is the progression of both the color and the translucence from the cervical to the incisal region. The cervical region generally has a coloration that tends toward reddish and is a bit transparent. The prior art provides no or only minimal accommodations for this graduation.
The object of the invention is therefore to provide a shade determination apparatus and a corresponding method that are able to provide a tooth or a dental restoration in an aesthetically pleasing manner, whereby the shade comparison is made substantially easier for the dentist and in particular the coloration and translucence obtained matches adjacent teeth or adjacent regions.
This object is achieved in accordance with the apparatus and method of the present invention. In particular, the shade determination apparatus has a set of reference templates for comparison to a patient""s tooth, whereby based on the coloration of the reference template the shade of a tooth or a restoration that is to be employed can be determined. The reference templates are produced in a layer arrangement, taking into consideration layer thickness and/or material selection, that corresponds to the tooth, dental restoration, or filling that is to be employed. The apparatus also has a storage apparatus in which the coloration of the reference template is stored and the layering of the tooth or dental restoration can be matched and determined based on partial images from an image of the patient""s tooth. In the method, a set of reference templates is compared to a patient""s tooth and based on the coloration of the reference template, the shade of a tooth or restoration that is to be employed can be determined. The reference templates are produced in a layer arrangement taking into consideration layer thickness and/or material selection that corresponds to the tooth or dental restoration that is to be employed. The coloration of the reference template is stored and the layering of the tooth or dental restoration can be matched and determined based on partial images from an image of the patient""s tooth.
Surprisingly, the inventive measures make it possible for the first time to obtain adequate coloration, even in terms of perception of the human eye, for the tooth to be replaced or for dental restorations. This is based in particular or the fact that the reference templates are provided with layer thicknesses that correspond to the actual layer thicknesses of the incisal material and dentin material to be applied. Surprisingly this measure makes it possible to obtain a more natural appearance, even when the reference template is not in the shape of a tooth, because by recording the image with the same camera, the same assessment flows into the process for analyzing the natural tooth and the reference template. It is obvious that in this context it is important to reference the shades if the same camera is not used but an identical model camera is used. In order to prevent metamerism effects it is advantageous to provide identical lighting.
In accordance with the invention, it is advantageous to select the layer thicknesses to correspond to the layer thicknesses that occur in practice. For instance, a set of reference templates can be produced with layer thicknesses: incisal material 0.2 mm, dentine 1 mm, and opaque layer 0.1 mm. An additional set of reference templates can be produced with the layer thicknesses: incisal material 0.2 mm, dentine material 0.3 mm, and opaque layer 0.1 mm. An additional set can be produced with the layer thicknesses: incisal material 0.15 mm, dentine 0.4 mm, deep dentine 0.3 mm, and opaque layer 0.1 mm.
In accordance with the invention, it is particularly advantageous in this context that the different colorations can be matched by means of automatic comparison. It is preferable in this context for the recorded natural tooth to be displayed on the screen and sections of this tooth to be marked in a suitable manner, and then to find the correct reference template immediately, selecting the reference template as appropriate. In accordance with the invention it is particularly advantageous for the reference templates to have been fired from original materials in the original layer thickness, cost-related issues not having a negative impact thereupon. On the contrary, it is no longer necessary to divide up shade guides oneself; rather, reference templates can simply be produced with laboratory quality, the appropriate detectable parameters for the reference template then being recorded with a reference camera and stored in a data base. Even if procurement of the recording apparatus and the necessary software represents a certain monetary outlay, modified shades obtained in new materials or other types of shades can then be made available to the dentist or dental technician with no other measures required.
The accuracy of the comparison can be performed in accordance with the invention depending on the number of reference templates available in the data base such that differences are no longer visible. In accordance with the invention, it is advantageous when the regions of the tooth to be analyzed are pre-specified as the regions that are generally particularly critical. When the dentist wants to deviate from the standards, this can be done with no further action required by selecting other surfaces, whereby it is understood that the dentist also pre-specifies the type of material he wants, e.g. plastic or ceramic, and also pre-specifies whether or not an opaque layer will be used for facing metal frameworks.
In accordance with the invention it is particularly advantageous that the shade determination apparatus determines the layers in terms of material selection, layer thickness, and combination of materials for every section of the tooth or tooth restoration that is to be blended in with the analyzed natural tooth. Thus the dental laboratory obtains precise information about how the restoration should be performed. It is also possible to pre-select the complexity of each different stage. For instance, a switch can be provided for xe2x80x9ccomplexxe2x80x9d and xe2x80x9csimplexe2x80x9d, which switch then pre-specifies more complex or simpler layers, as desired.
An additional parameter that must be determined for the dentist""s or dental technician""s comparison to the reference template is the layer thickness that will be available to him for a restoration. In this case as well there is an automatic comparison with the best option, since the reference templates are available in different overall layer thicknesses so that the different shades can be taken into account and included automatically in the assessment.